ABSTRACT
This chapter discusses the relatively ordered structure of crystalline solids, and discusses some aspects of the less ordered structures of ceramics and polymers. Many construction materials, particularly metals and some ceramics, consist of small crystals or grains within which the atoms are packed in regular, repeating, three-dimensional patterns giving a long-range order. Crystals are formed in a cooling liquid. In the liquid the atoms are in a state of constant motion and change positions frequently. The chapter argues that atoms are hard spheres – a considerable but convenient simplification. Point defects occur at discrete sites in the atomic lattice and can be either missing or extra atoms, called vacancies or interstitial atoms respectively. A substitutional impurity occurs when the foreign atoms take the place of the parent atoms, resulting in a substitutional solid solution. The backbone of the chain normally consists of covalently-bonded carbon atoms.
